I had heard that the rope lite thing had to be spaced far apart or it got too hot before I made my set up.
They do put out some heat.
I found that you HAD to put the ones I had as far apart as they said too or they got too hot.
I did the lites covered with sand method which might be different than the other methods.( I put the lites in a box and cover them with sand.).
I eventually used Pomice instead of sand.
I originally got the 2 strings but found I only needed 1 for what I needed to use for the heat and size box I had.
I Did run the set up before I put my seeds over it to see what the temp. was(used a thermometer that kept the high and low for 24 hours)).
Not everything on the internet is cool.
A lot has to do with stuff working the way the poster used it,any variation makes a LARGE difference.
That is why I pre tested it first.
Wasting expensive seeds on something you haven't tried before isn't the best way to go.
I also put a mini greenhouse on it,not the zip lock type germination thing.
I think if I put zips and coffee filters on it I'd have cook the seeds,not enough stuff to heat up.
Heating several 72 cell mini greenhouse worked great.
I stopped using the rope lite thing because I lost my garden space and the setup was too big for what I needed to sprout.
I went from 400+ plants 2X a year to 80 plants 2X a year.
I now use a thermostat with heat mats placed on foam now.
72 cell foam insulation set up.
Rope lites heat a bigger area than I need.
Even Heat mats on a shelf get too hot or stay too cold without a thermostat.
They try to heat up whatever they are sitting on and run 24/7.
If the grow area is cold you don't get the temps you want.
If set on an insulator(foam/grill/non heat conductive surface they work better).
The probe is in a cell and all the heat goes to the mini greenhouse,not to heat or try to heat up the shelf the heat source is sitting on.
Any heat source has it's own use.
I know people who put their seeds on their modem,mine gets and stays way too hot.
The fridge top gets hot and cold....
Whatever you try should be tested out first.
Just because something worked for me it might not for you.My set up might get more attention by me than yours or whatever.